This invention relates to a method for effectuating a coronary artery bypass.
Coronary arteries frequently become clogged with plaque which at the very least impairs the efficiency of the heart""s pumping action and can lead to heart attack. The conventional treatment for a clogged coronary artery is a coronary by-pass operation wherein one or more venous segments are inserted between the aorta and the coronary artery. The inserted venous segments or transplants by-pass the clogged portion of the coronary artery and thus provide for a free or unobstructed flow of blood to the heart.
Such conventional coronary artery by-pass surgery is expensive, time-consuming, and traumatic to the patient. Hospital stay subsequent to surgery and convalescence are prolonged.
A new coronary artery by-pass technique is disclosed in U.S. Pat. No. 5,429,144. That technique utilizes a stent made of a biocompatible material and comprises steps of moving the stent in a collapsed configuration through a blood vessel of a patient""s vascular system to the patient""s heart, inserting the stent in the patient""s myocardium so that the stent extends at least partially through the myocardium and only within the myocardium, and upon the disposition of the stent in the myocardium, expanding the stent from the collapsed configuration to a substantially tubular expanded configuration so that a blood flow path is formed at least partially through the myocardium.
Pursuant to U.S. Pat. No. 5,429,144, the stent may be disposed in the myocardium so that it extends only partially through the myocardium, from a coronary artery, upstream of a vascular obstruction, or from the left ventricle of the heart. Alternatively, the stent may extend completely through the myocardium to establish a blood flow path from the left ventricle to a coronary artery, downstream of a vascular obstruction. In any case, the stent is deployed so that it extends only within the myocardium and does not protrude beyond the heart tissues, either into the left ventricle or into the coronary artery.
Where the stent of U.S. Pat. No. 5,429,144 extends only partially through the myocardium and thus terminates within the cardiac tissues, the stent guides blood directly into the heart tissues and particularly into cardiac vesicles which naturally occur in the myocardium. The blood is naturally distributed from the vesicles into the cardiac tissues and is collected by the veins of the heart. Where the stent terminates within the myocardium and extends from a coronary artery, upstream of a vascular obstruction, the stent maintains its expanded form during diastole, so that blood pumped from the heart is forced into the stent and from thence into the cardiac tissues. Where the stent terminates within the myocardium and extends from the left ventricle, the stent may collapse during systole, under the compressive forces exerted by the contracting heart muscle. In that case, blood is delivered to the myocardium during diastole: blood flows into the stent from the left ventricle as the ventricle is filling with blood. Alternatively, where the stent terminates within the myocardium and extends from the left ventricle, the stent may maintain its expanded form during systole, despite the compressive forces exerted by the contracting heart muscle. In that case, blood is forced into the stent and from thence into the cardiac tissues during heart contraction.
According to U.S. Pat. No. 5,429,144, the coronary bypass method further comprises inserting a distal end portion of a catheter into the perforation or recess prior to the ejection of the stent, and sensing pressure on the catheter along the distal end portion, thereby determining a thickness of the myocardium at the perforation or recess. The stent is cut from a piece of stent material so that the stent has a length corresponding to the sensed or measured thickness of the myocardium at the perforation or recess.
U.S. Pat. No. 5,429,144 describes the use of a drill head during diastole to cut a perforation into the myocardium. The synchronization or coordination of the drilling and stent ejecting steps with heart action is implementable by computer. Where the stent is disposed in the myocardium so that the stent extends only partially through the myocardium from the patient""s left ventricle, the stent is inserted into the myocardium from the left ventricle. Accordingly, a distal end of the catheter is passed into the left ventricle prior to the deployment of the stent, while the stent is moved in its collapsed configuration through the catheter and into the left ventricle of the heart.
An object of the present invention is to provide an improved method for forming a coronary artery by-pass to thereby enable the oxygenation of cardiac tissues.
Another object of the present invention is to provide a method for forming a coronary artery by-pass which does not require leaving a device in the patient.
A further object of the present invention is to provide such a method which is less invasive and less traumatic to the patient than conventional by-pass surgery.
Basically, the present invention is directed to a stent-less coronary artery by-pass wherein one or more recesses are formed in the myocardium. The recesses open sufficiently during diastole to permit blood flow into the myocardium and the vesicles therein.
A cardiovascular treatment method in accordance with the present invention utilizes an elongate flexible surgical instrument (e,.g. catheter) having a distal end. A distal end portion of the instrument is inserted into a vascular system of a patient. A surgical head at the distal end of the instrument is positioned so that the head is disposed adjacent to myocardium tissue of the patient. The head is operated to form a recess in the myocardium tissue. Prior to operating the head to form the recess, a thickness of the myocardium tissue is measured, the recess formed during the operation having a length determined in accordance with the measured thickness of the myocardium tissue. The thickness measurement partially determines the length of the recess. The angle of entry of the recess with respect to the heart wall also partially determines the length of the recess: the greater the angle, the longer the recess can be for a given myocardium thickness.
The thickness of the myocardium may be measured by generating an ultrasonic pressure wave, sensing reflected pressure waves and analyzing the reflected pressure waves to determine the thickness. The ultrasonic pressure wave generator (e.g., a piezoelectric crystal) and the ultrasonic wave sensor (also a piezoelectric crystal) may be disposed in the catheter wall at the distal tip thereof, or at the distal tip of an ancillary instrument inserted through a lumen of the catheter.
Measuring the thickness of the myocardium may be implemented by operating a computer aided tomography scanning machine, a magnetic resonance imaging machine or an echocardiogram device.
Generally, it is contemplated that the recess terminates in the myocardium tissue and is formed from the left ventricle of the patient. Accordingly, the surgical head is disposed adjacent to an inner side of the myocardium tissue, inside the left ventricle, so that the recess extends from the left ventricle.
According to a feature of the present invention, the surgical head is a contact laser tip. In that case, operating the surgical head includes transmitting monochromatic coherent electromagnetic radiation (laser energy) through the contact laser tip to the myocardium tissue. Alternatively, the surgical head may include a drill tip, the operating of the head including pushing the drill tip into the myocardium tissue and rotating the drill tip during the step of pushing.